Alzheimer's neurofibrillary tangles are penetrated by astroglial processes and appear eosinophilic in their final stages.

Alzheimer's neurofibrillary tangles (ANT) in the hippocampal area were studied immunohistochemically using antisera against glial fibrillary acidic protein (GFAP) and S-100 protein in 48 patients with or without dementia between 52 and 92 years old. In 27 of the 38 brains that developed ANT in the hippocampal area, some ANT were immunostained with these antisera. Flame-shaped or globose-shaped immunostains were occasionally continuous with astroglial cell bodies and processes. They appeared particularly in the entorhinal cortex, subiculum and CA1. The ANT, immunostained with GFAP and S-100 antisera, apparently correspond to slightly eosinophilic tangles in H&E sections and to less argentophilic tangles in silver-impregnated sections in all of the 27 brains. ANT of another 11 brains were consistently negative with these antisera. The GFAP-positive eosinophilic tangles were encountered in the brains of older patients (P less than 0.01) and with more abundant formation of ANT (P less than 0.001). This alteration was present in all of the 20 brains with more than 100 ANT per section and none of the eight brains with less than 10 ANT. These findings suggest that in the last stages, ANT are penetrated by eosinophilic processes of astrocytes, and appear eosinophilic, and that the presence of GFAP-positive eosinophilic tangles indicates the abundant formation of ANT.